Regenerative type transmissions are generally well known in the art. U.S. Pat. No. 4,126,200 to Miller et al, for example, teaches a two-mode, input-slip, integrated hydrostatic unit for use as a vehicle drive system. Miller et al discloses a drive system for vehicles powered by heat engines. More particularly, the Miller et al arrangement constitutes a drive and transmission system providing kinetic energy storage for use in a vehicle powered by a heat engine such as an internal combustion engine. Specifically, Miller et al teaches a vehicular drive system that includes a combination of a heat engine, flywheel, an electric motor/generator and a differential. The heat engine is directly coupled to a flywheel and to the first shaft of a differential. The motor/generator is coupled to the second shaft of the differential, and the third shaft of the differential is connected to a multi-speed gearbox. The gearbox output is connected to the drive wheels of the vehicle. By controlling the torque produced by the electric motor/generator and the fuel supply to the heat engine, the flywheel can be made to decelerate during vehicle acceleration and to recover energy during vehicle deceleration. During operation of the vehicle, the heat engine is directly coupled to the flywheel at a fixed gear ratio.
In the first operational mode of the Miller et al drive system, the flywheel and the source of rotational energy are coupled to the first drive terminal and the second drive terminal is coupled to the drive wheels of the vehicle. In the second mode of operation, the flywheel is coupled to the second drive terminal, and the rotational energy source and the first drive terminal are coupled to the drive wheels. Finally, the control apparatus for governing the operation for the variable transmission apparatus and the source of the rotational energy is capable of independent control of the speed of the flywheel and the source of the rotational energy.
The Miller et al transmission system featured several new innovations. For example, the source of rotational energy and the flywheel were not directly coupled at a fixed gear ratio in all of the modes. Thus, the rotational velocity of the flywheel could be a varying multiple of the engine speed during the starting mode of the flywheel energization, as well as operation in the "low", "second" and "hi" (or highway) modes of operation, and a desired fixed multiple thereof during directly coupled operation of the flywheel and engine in the first mode of operation. As a result, Miller et al employed only a single variable transmission operable in a number of differing modes to govern: the speed relationship between the flywheel and the rotational energy source; and, the speed relationship between the flywheel and rotational energy source on one hand and the vehicle wheels on the other. This arrangement enabled independent control of the rotational speed and torque of the flywheel and rotational energy source so that the operation of the flywheel and rotational energy source could be governed in a manner that produces improved efficiency and fuel economy under differing driving conditions.
However, the Miller et al drive system has several drawbacks. These drawbacks include the use of a hydrostatic unit which is bulky and cumbersome when used in conjunction with a transmission system. Moreover, the Miller et al drive system was still not as efficient as it could be. These drawbacks were addressed in U.S. Pat. No. 5,024,633. Generally, the '633 patent discloses an improved power transmission wherein an engine is selectively coupled to an output drive member through a gear and hydrostatic transmission arrangement so that an energy storage device is selectively coupled with the engine gearing arrangement and hydrostatic transmission to selectively store energy from the system, and then deliver energy back to the system. This arrangement allows the size of the hydrostatic units to be reduced in size, while maintaining the efficiency of the transmission.
Unfortunately, the use of hydrostatic arrangements in transmission systems creates numerous design problems. For example, hydrostatic pumps and motors do not lend themselves to a concentric transmission design. Further, hydrostatic units cannot accept another shaft operating concentrically through their pump and motor shafts. As a result, the hydrostatic pump and motor must be set laterally to the side along, at best, a parallel centerline with external gearing so as to transfer the power provided by the hydrostatic arrangement to the centerline of the transmission, thus making the transmission bulkier than desired. In addition, hydrostatic units that operate in excess of 5,000 PSI tend to be very noisy.
Accordingly, there is a need in the art for a regenerative transmission system that is efficient in operation and can receive multiple power inputs from highly differing sources.